1. Field of the Invention
The present invention relates to the method of manufacture of a foamed core article with a Class A visible surface and with integral structural reinforcements on the non-visible back surface beyond current manufacturing capabilities.
2. Background Art
Designers often use plastic parts as replacements for metal parts to take advantage of the greater design freedom that molded parts can give and to reduce the weight and cost of an article. The injection molding process is used to produce such plastic articles. But when injection molding relatively large articles, such as heavy truck fascias, the clamping force needed to seal the mold and to inject the amount of plastic material that is required to fill the mold cavity, requires tremendous pressures to produce a usable part. Injection molds and molding machines that can produce these parts are very large and heavy and are extremely expensive to acquire and to operate. These pieces of capital equipment must routinely be amortized over the number of pieces that are produced therein. To date, the costs have been greater than heavy truck manufacturers have been willing to incur for their short run, low volume programs. As a result, manufacturers have either limited the size of the parts that are injection molded or they have opted for other, less expensive, processes to produce the large parts.
In an effort to injection mold large parts without the full expense that is required for normal injection molds and machines, manufacturers have produced large functional plastic parts by injecting a molten mixture of plastic and a blowing agent into a mold cavity. By adding a foaming agent to the plastic resin during injection molding process, the foaming action creates localized internal packing pressure that forces the melt to fill the part cavity. The addition of the foaming agent to the molten resin expands the volume of the injected melt and thereby reduces the amount of material used, per shot. By reducing the density of the melt, the weight of the article that is molded is also reduced. A further benefit of adding blowing agent to the melt, with the resulting foaming action in the cavity, is that the need for extreme external injection pressure and the related clamping pressure, to keep the mold closed, is greatly reduced. The net result is that a high-pressure molding process is now converted to a low-pressure molding process. Despite these benefits, there are drawbacks that prevent the foamed plastic process from being widely used to manufacture Class A structural parts. These are:                the internal packing pressures of the foamed plastic process do not always yield surfaces that are free of surface porosity and local shrinkage deformities, and        because the foam swirls on the surfaces of the molded part, the foamed plastic process is not capable of yielding the desired Class A surface that is necessary for visual parts.        